Motorcycles have changed a lot over the years. Here are five that we think are the best classic parallel twins.

Triumph Bonneville

Possessed of probably the best-looking motorcycle engine of all time and named after the salt flats at which it broke the world two-wheeled land speed record, it's no wonder the new Triumph company has resurrected the badge in recent years.

BSA Spitfire

Less visually interesting than the Bonnie's engine, the A65 twin was slightly more powerful, albeit more vibratative and marginally less reliable. Like the Triumph, it was successful on US flat tracks and in desert racing during the 60s, as the BSA Hornet.

Norton Dominator

From 500cc, to 750cc, the Dominator engine was eventually tilted forward and further enlarged for the Commando, but was at its best as the 650 SS. Visually more genteel than the Bonnie and Beezer, but a very successful racer, especially on the road.

Kawasaki W1

It's exactly what it looks like, a copy of BSA's 1950s A10 twin, but with better oil-scavenging, and reliability and a five-speed gearbox. It was all too short-lived but its spirit lives on in the form of Kawasaki's excellent modern W650 and W800 models.

Yamaha XS1

Starting off in basic form, this 650cc twin was later offered as a tasteful ''production custom'' design. Like its British counterparts it had great dirt track and desert success, being ridden for a while by the great Kenny Roberts. A great restoration project.